CN108462151B

CN108462151B - Method and arrangement for protecting an electric motor against overheating

Info

Publication number: CN108462151B
Application number: CN201810151549.9A
Authority: CN
Inventors: T·施塔克穆特; M·胡博-克莱斯; M·厄特迈尔; D·诺瓦克
Original assignee: Wilo SE
Current assignee: Wilo SE
Priority date: 2017-02-20
Filing date: 2018-02-14
Publication date: 2020-12-08
Anticipated expiration: 2038-02-14
Also published as: DE102017001560A1; EP3364512B1; CN108462151A; EP3364512A1

Abstract

The invention relates to a method for protecting an electric motor (1), in particular of a centrifugal pump assembly, against excessive temperatures, wherein the voltage supply (9, 11) is interrupted in the event of an error by opening a tripping mechanism (14, 17). In this case, a motor current (I) received by the electric motor (1) is determined and checked_M) And/or variables (U) associated therewith_s) Wherein when the motor current (I)_M) And/or variables (U) associated therewith_s) Above a certain limit value (I) for a certain uninterrupted period of time or for a plurality of interrupted periods of time_M,lim) When the maximum motor current (I) is lower than the limit value, the interruption is performed_max) Or with the motor current (I)_M) Related variable (U)_s) To a value corresponding thereto. This makes it possible to indirectly derive the motor temperature without using temperature sensors in the motor windings.

Description

Method and arrangement for protecting an electric motor against overheating

Technical Field

The invention relates to a method and a circuit arrangement for protecting an electric motor, in particular of a centrifugal pump unit, against excessive temperatures, wherein the voltage supply is interrupted in the event of an error by opening a switching-off mechanism.

Background

Various disturbances may occur during operation of the electric motor, which disturbances may be caused by an abnormal heating of the motor windings of the electric motor. An example of this is jamming of the motor shaft to which the motor will respond with a maximum motor current in order to be able to apply a maximum torque and put the motor shaft into rotation. Another example is a short circuit in the power electronics, by which a short circuit current flows through the motor windings without the electric motor rotating. Since the heat generated in the motor windings by the high motor current is transferred to the motor housing, there is then a danger of burning for the user on the outside of the motor housing. In order to prevent the risk of burns, temperature limit values are defined in different guidelines and standards, for example IEC60335 chapter 19, which the electrical products must comply with in order to gain entry in europe or other markets.

It is known in electric motors to measure the motor Temperature via a Temperature sensor, for example a PTC (positive Temperature Coefficient thermistor) or other Temperature-dependent resistor, which is arranged in the stator in the vicinity of the motor windings, in order to detect the winding Temperature. Fig. 1 shows such an arrangement. The output signal of the temperature sensor 2 here directly controls the shut-off relay 14. Via and gate 15, said output signal is coupled to a second output signal of control unit 10, which normally signals no error. If any monitoring error occurs, the value of the second control signal is changed. If an excessive temperature occurs, the value of the output signal of the temperature sensor is changed and a temperature alarm is signaled. In both cases, the value of the output of the and gate 15 is therefore changed, and the tripping relay 14 is therefore lowered, so that the electric motor 2 is disconnected from the mains supply 11 and is switched into a safe operating state. This solution for protecting against excessive temperatures is purely hardware-based and thus fast, reliable and robust. However, the presence of the temperature sensor 2 makes the electric motor expensive. The wiring and arrangement of the temperature sensors in the stator of the electric motor 1 results in a more complex structure and a more difficult installation of the electric motor.

Disclosure of Invention

The object of the invention is therefore to provide a structurally simpler protection of an electric motor from excessive temperatures, which is likewise reliable, rapid and safe.

The object is achieved by a method for protecting an electric motor against overheating and by a circuit arrangement.

The invention is based on the recognition that the winding temperature is substantially dependent on the current flowing in the winding (R.I.)_M ²) However, it is also dependent on the ambient temperature and, in particular, also on the temperature of the medium being conveyed in the case of wet-running motors which drive the heating circulation pumpIn this connection, the temperature can be higher than 100 ℃ in the case of a heat transfer medium. If the medium temperature exceeds the ambient temperature of the electric motor, the ambient temperature can be ignored. And vice versa. The medium temperature or the ambient temperature shows some kind of deviation with respect to the winding temperature. It has furthermore been recognized that a defined motor current causes a defined, limited temperature increase of the winding temperature, as is shown in fig. 4 and 5. In said fig. 4, curve K1 shows the ambient temperature, which fluctuates around approximately 70 ℃. Curve K2 shows the medium temperature, which fluctuates between 107 ℃ and 110 ℃. Current curve K3 ═ I_M(t) included mutations to 250mA, 300mA, and 350 mA. Each sudden change in the motor current leads to a limited increase in the winding temperature K4 ═ θ (t), in which the winding temperature K4 approaches the determined temperature progressively over time, approximately 143 ℃ in the case of 250mA, approximately 162 ℃ in the case of 300mA, and approximately 188 ° in the case of 300 mA. Of course, said values are related to the structure and type of the motor, in particular to the dimensions of the stator and thus to the thermal capacity, but are characteristic for a determined electric motor and determinable on the factory side. Thus, each motor current can correspond to a particular winding temperature.

In order to protect the electric motor from overheating in accordance with relevant guidelines and standard measures, an exact knowledge of the current motor temperature is not important. Rather, it must be absolutely ensured that: in particular, a defined maximum motor temperature is not exceeded outside the motor housing and in the windings in order to avoid the risk of burns. By means of the knowledge obtained beforehand, each motor current can correspond to a determined winding temperature, able to correspond to a determined limit temperature θ_limConversely, the corresponding limiting current I is determined_M,limServing as a temperature sensor for said limit temperature theta_limReference to (3). Significantly, the limit temperature θ_limBelow the maximum allowable motor temperature theta_maxWherein the maximum allowed motor temperature is preset according to the protection level. At the maximum motor temperature allowed to last theta_maxIn the case of 190 ℃, the limiting temperature can be θ, for example_lim160 ℃ or 165 ℃.

Fig. 5 shows that in the case of an electric motor with a larger stator than in fig. 4, the motor current abruptly changes to 400mA, wherein the motor temperature in this case rises (only) to approximately 163 ℃. Subsequently, the motor current abruptly changes to its maximum value I_M,limThe maximum here is, for example, I_M,lim750mA, where the motor temperature rises sharply to a value above 200 ℃. This increased increase in winding temperature K4 is shown in fig. 6. It is clear that the time period R continues until the maximum current I_M,limHeating the winding to a maximum temperature theta_max. In the example of fig. 6, the time period R is about 20 s. However, depending on the motor type and maximum temperature θ_maxAlternatively, the time period can be shorter or longer. This therefore means that: even the maximum motor current I_M,limIt is allowed to absolutely exist a certain time without the electric motor becoming inadmissibly hot. Of course, the energization of the motor windings must be switched off at the latest after a period of time has elapsed in order to avoid heating to an inadmissibly high motor temperature, i.e. to avoid overheating. Thus, the period R represents a response period R for taking effective protective measures.

The invention therefore proposes a method for protecting an electric motor, in particular of a centrifugal pump assembly, against excessive temperatures, in which the voltage supply is interrupted in the event of an error by opening a shut-off mechanism, wherein the motor current received by the electric motor and/or variables associated therewith are determined and checked, and the interruption is carried out when the motor current and/or variables associated therewith are above a certain limit value, which is less than the maximum permissible motor current or the value of the variable associated therewith, within a certain uninterrupted period or within a plurality of defined interrupted periods.

Therefore, according to the invention, a circuit arrangement for protecting an electric motor, in particular of a centrifugal pump assembly, against excessive temperatures is also proposed, which comprises: a circuit breaking mechanism for interrupting the voltage supply in the event of an error; measuring means for determining a motor current received by the electric motor and/or a variable related thereto; and a control unit for checking the motor current or a variable related thereto, wherein the control unit is set up to control the shut-off mechanism such that the voltage supply is interrupted if the motor current and/or the variable related thereto is/are above a defined limit value for a defined uninterrupted period of time or for a plurality of interrupted periods of time, the limit value being less than the maximum permissible motor current or a value of the variable related to the motor current corresponding thereto. It is significant that the limit value is also greater than the nominal current (rated current) of the motor.

This way it is possible to prevent: the excessive temperatures generated on the motor, which at the same time is simpler in terms of structural construction and component mounting, result in the electric motor satisfying the relevant criteria and regulations without the use of temperature sensors here.

In order to achieve a sufficiently long response time, for example a response time between 10s and 20s (permissible error time), the limit value can lie between 10% and 90% of the maximum motor current, in particular between 1/3 and 2/3.

For an electric motor with an allowed maximum motor current of 750mA, the limit value can therefore be between 300mA and 400mA, for example. The same applies to the variable relating to the motor current for which the limit value can be a value between 1/3 and 2/3 corresponding to the maximum motor current. Preferably, the limit value can correspond to an extreme motor current which, without interrupting the application of the extreme motor current, does not exceed a defined limit temperature θ_lim. This can be determined for the electric motor on the factory side. Thus, with the example of FIG. 5, at θ_limAt a defined limit temperature of 160 ℃, the maximum motor current that can be applied without interruption is at or slightly below 400mA, for example 390 mA. Here again, the same applies to the limit values of the variables associated with the motor, which can be values corresponding to the determined maximum motor current.

By suitable selection of the response time period or the sum of the individual time periods, it is possible to: not exceeding maximum allowableThe motor temperature of (1). To ensure this, as shown in fig. 6, the time period can correspond to or be less than a time period of: the time period is from the limit temperature theta under the condition that the maximum motor current flows_limUntil the maximum permissible temperature theta of the electric motor is reached or is about to be reached_max. The time period can be determined on the factory side of the electric motor.

If the motor current or a variable associated therewith reaches a limit value, it is simply assumed according to the invention that: the motor temperature has reached or at least will soon reach the limit temperature. If the current or the variable remains within the limit value, this is in principle insignificant, since the motor current, in terms of the magnitude of the limit value, does not lead to critical motor temperatures even with continuous application, and at most only to limit temperatures. In the case of the example of fig. 5, more than 20 minutes are also required for this total attribution. However, even in the case of a slight exceeding of the limit value, the overheating protection according to the invention is already initiated and the interruption of the voltage supply is caused within a defined time period even in the presence of this motor current which is slightly above the limit value, since in the method according to the invention the actual magnitude of the motor current is not taken into account. Therefore, it is not important for the present invention whether the limiting current exceeds 1mA, 10mA or 100 mA. Thus achieving the greatest degree of security.

In order to be able to realize a particularly simple implementation of the monitoring of the response time period, a counter can be used.

According to one embodiment variant, the counter can be an up-counter which is incremented when the motor current and/or a variable associated therewith exceeds a limit value, and the voltage supply is interrupted when the counter reaches a maximum counter reading.

Alternatively, the counter can be a down counter (Countdown) which is decremented from a maximum counter reading when the motor current and/or variables associated therewith exceed a limit value, and the voltage supply is interrupted when the counter reaches a value of zero.

With regard to the advantageous refinements described below relating to the up counter, it is noted that the opposite direction of action for each individual refinement of the down counter can likewise be implemented according to the invention. Here, the increase of the up counter corresponds to the decrease of the down counter, and the decrease of the up counter corresponds to the increase of the down counter. The maximum counter reading of the up counter will correspond to the zero value of the down counter and the zero value of the up counter corresponds to the maximum counter reading of the down counter.

According to one embodiment variant, the counter can be a digital counter that increases or decreases in an integer manner. However, according to an alternative embodiment variant, the counter can also be a rational counter of defined precision, which is incremented or decremented in steps different from the value of the integer, for example in steps of 0.5 or 0.1.

The incrementing or decrementing of the counter can be carried out within the scope of a cyclic enquiry as to whether the motor current or a variable associated therewith exceeds a limit value. The change of the counter, which is incremented or decremented per unit time or per cycle, is thus constant.

Alternatively, the counter can be determined or calculated by integrating the motor current or a variable related thereto, as long as the motor current or the variable is above a limit value. In this case, the increment of the counter per unit time is related to the value of the motor current or variable exceeding the limit value. The incrementing of the counter is therefore carried out continuously or quasi-continuously within a defined accuracy range (position after the decimal point) up to the maximum counter reading.

The counter can be implemented in hardware or software. Here, software is preferable so that other components are not necessarily used. However, the implementation of hardware techniques has the following advantages: which is particularly reliable, robust or non-time critical. In terms of hardware technology, the counter can be implemented in analog or digital technology. Mathematically, the counter therefore represents a summation or an integration, enabling implementation in hardware or software by means of an adder/subtractor or an integrator.

In addition to the temperature rise of the electric motor, cooling thereof is also considered. If the motor temperature rises to a value above the limit temperature in advance because the motor current is in or above the height of the limit value, and then the motor current is reduced again to a smaller value, the motor temperature also drops again. This can be taken into account according to the invention in the case of an up counter as follows: when the motor current and/or the variable related thereto is below a limit value, the counter is decremented. In the case of a down counter, cooling can be considered according to the invention as follows: the counter is incremented when the motor current and/or the variable associated therewith is below a limit value, in particular only when it is less than a maximum counter reading.

The incrementing of the up counter or the incrementing of the down counter does not have to take place here at the same magnitude per unit time as the incrementing of the up counter or the decrementing of the down counter, since cooling also takes place more slowly than heating.

In the case of an up counter, the step by which the counter is increased per unit time, in particular incremented per cycle, when a limit value is exceeded can therefore be greater than the corresponding step by which the counter is decreased per unit time, in particular decremented per cycle, when a limit value is undershot. Accordingly, in the case of a down counter, the step by which the counter X is decreased per unit time, in particular decremented per cycle, can be greater than the corresponding step by which the counter is increased per unit time, in particular incremented per cycle, in the case of a value below the limit value.

In the case of a digital counter, the change can be effected in a simple manner as follows: when the motor current or a variable related thereto is below a limit value, an up counter is incremented in each cycle or a down counter is decremented in each cycle.

If the counter is implemented as an integral of the motor current or of a variable associated therewith, the integration can simply be continued, which is then carried out as a function of the negative difference of the motor current or variable from the limit value, so that the value of the integration is reduced again as a result of the integration. The reduction of the counter is only and/or often meaningful when the counter is positive. Since a negative counter would mean that the motor temperature is below the limit temperature and thus an erroneous starting value is formed when the motor current again reaches the limit value. Thus, the counter is meaningfully decremented only when the counter is greater than zero.

The following may occur: the motor current or a variable related thereto rises again above the limit value before the up-counter reaches the zero value or the down-counter reaches the maximum value. In this case, the up counter is simply incremented again or the down counter is decremented. The current counter value thus repeatedly forms the starting value for the temperature monitoring according to the invention. The starting value when the up-counter is greater than zero or the down-counter is less than the maximum value represents: since the motor current is above the limit value, the previous heat input has not yet been completely removed again. The thermal history of the motor windings is therefore also taken into account by means of the starting value corresponding to the last counter reading.

The following may occur: although the maximum counter reading or zero has not been reached in a single uninterrupted period, the sum of the counter increments over a plurality of interrupted periods causes the maximum counter reading to be exceeded or the counter decrements over a plurality of interrupted periods causes the sum to fall below zero, since the heat input between the periods above the limit is not completely eliminated.

As already mentioned, the interrupts can be implemented in a software-controlled manner. The implementation of the method according to the invention can be carried out in a motor control device which is generally provided for setting and/or regulating the rotational speed of an electric motor. This has the following advantages: no additional hardware is required to implement the method. The comparison of the motor current and/or the variables related thereto with the limit values can be performed periodically in software. For example, the cycle can be performed or repeated every 10ms to 250ms, preferably every 50ms or 100 ms. The counter is then incremented or decremented depending on the result of the comparison.

To consider: the electric motors have different heating and cooling rates, and the steps by which the up-counter is increased per unit time, in particular incremented per cycle, can be larger than the steps by which the up-counter is decreased per unit time, in particular decremented per cycle. Furthermore, the step size of the down counter decreasing per unit time, in particular decrementing per cycle, can be larger than the step size of the down counter increasing per unit time, in particular incrementing per cycle.

Preferably, the interruption of the voltage supply to the electric motor can only be cancelled again if the counter is below a percentage value of the maximum counter reading in the case of an up-counter or above a percentage value of the maximum counter reading in the case of a down-counter. Thus, according to the improvement, it is provided that the switching off of the voltage supply or the switching off of the motor winding is reversible, so that a permanent unavailability of the electric motor is not caused. Rather, it is provided that the electric motor can be operated again or even started again when the motor windings cool to a certain value. Physically, hysteresis is thereby achieved.

Said percentage value of the maximum counter reading can for example lie between 30% and 80%, preferably approximately or at least 50% or lie between 50% and 70%. The improvement also shows: the monitoring of the motor temperature and the counting of the counter also continue after the voltage supply is interrupted.

According to one embodiment variant, the counter reading can be stored in a non-volatile memory. This has the following advantages: when the counter reading is required, it can be used at any time, in particular also after switching off the electric motor manually or automatically due to an error. Therefore, the counter can continue to operate also during the interruption of the voltage supply. In other cases, the "memory" of the counter is also eliminated by cutting off the power supply to the motor electronics. Preferably, the stored counter reading can be used as a starting value for the counter when establishing, in particular restoring, the voltage supply to the electric motor. If, for example, the electric motor is disconnected from the grid shortly before the maximum counter reading is reached, the counter starts at zero when the counter is started next time, although the motor can still have a significant warm-up when started again. This is avoided by using the stored counter reading as a starting value for the counter.

As already detailed in advance, the response time period R is preferably selected such that the permissible maximum motor temperature θ is not exceeded in the response time period from the point of view of protecting the user against burns_max. Since the response period R is reflected in the magnitude of the counter reading, the maximum counter reading should correspond to or be less than a period from the limit temperature θ with the maximum motor current flowing therethrough_limContinues until the maximum permissible temperature theta of the electric motor is reached_max。

According to one embodiment variant, the disconnection means can be an electromechanical switch, in particular a disconnection relay, wherein the interruption of the voltage supply is caused by the opening of the electromechanical switch. The electromechanical switch is suitable in particular when higher currents or voltages have to be switched on. As an alternative to electromechanical switches, electronic semiconductor switches, in particular power electronic switches, such as IGBTs or IGCTs, can also be used.

Via the switch in its closed state, current can flow from the mains voltage supply to the electric motor. The electromechanical switch can be arranged in the input circuit of the electric motor, i.e. before the rotational speed setter and shortly after the mains voltage supply, so that the entire motor electronics is or becomes unpowered by interrupting the voltage supply (here the mains voltage supply). Alternatively, an electromechanical switch can be provided between the dc voltage intermediate circuit and the inverter of the rotational speed setter, so that the voltage supply (in this case the dc voltage supply of the intermediate circuit) is disconnected from the motor windings by opening the switch. In addition, the motor electronics remain powered here.

According to a further embodiment variant, the disconnection means can be a switching device, in particular at least one controllable semiconductor switch, for example a transistor, wherein the interruption of the voltage supply is brought about by opening the switching device. This is suitable in particular when lower currents or voltages are to be switched on. The disconnection mechanism is therefore dimensioned meaningfully.

Preferably, the electronic switching device causes an interruption of the voltage supply to the electric motor by interrupting the supply Voltage (VDD) to the drive circuit of the inverter which is fed to the electric motor in normal operation. Since the semiconductor switches of the inverter are no longer controlled by the drive circuit and remain switched off in the absence of the supply voltage. This also enables the current to be cut off to the motor windings. In the closed state of the switching device, the drive circuit is connected to the supply Voltage (VDD), in particular to the low-voltage supply, as required. Since only a minimum power is switched on in this case compared to a switching relay, the components required for switching on can be dimensioned particularly small and accordingly only a small installation space is required.

In an ideal case, the electronic switching device is realized by two individual switches, in particular two semiconductor switches, such as transistors, connected in series, which are actuated or controlled by a common control signal. This prevents the following risks: the voltage supply cannot be interrupted due to defects, for example short circuits in the component. Redundancy is provided by two individual switches.

In a suitable manner, the motor current and/or variables associated therewith are determined and checked in each operating mode of the electric motor and not only in normal operation, in particular also in a preparatory mode of operation, so that certain errors, for example damaged semiconductor switches in the inverter, can also be detected in the motor-off state.

For example, it can be provided that the semiconductor switches of the inverter, which feed the electric motor in normal operation, are individually switched on in sequence when the motor current and/or variables related thereto exceed a readiness limit value in the readiness mode of operation. This enables defective semiconductor switches to be identified. Since defects on a semiconductor switch are usually represented as short circuits between its line terminals (emitter-collector or drain-source). By sequentially, i.e. in turn individually switching on the semiconductor switches, it is checked that: whether a short circuit is generated on one of the full bridges. This is thus the case: in addition to the defective semiconductor switch in one half-bridge of the full-bridge, the other semiconductor switch in the other half-bridge of the full-bridge is placed in a conducting state. The intermediate circuit voltage is thus short-circuited across the two half-bridges. A short-circuit current thus flows, which can either blow the fuse ("self-destruction") or trigger the counter calculation according to the invention, which then, as long as the short circuit is maintained, initiates an emergency shutdown after a corresponding time due to an excessively high temperature.

According to one embodiment variant, the motor current can be measured. It is to be noted here that a direct measurement of the current itself is not physically feasible. The measurement of the current is always carried out via auxiliary variables, such as a voltage drop across a resistor through which the current to be measured flows or a magnetic field generated around a conductor through which the current to be measured flows. Preferably, also in the method according to the invention, the motor current is measured by the voltage drop across the measuring resistor, in particular by the shunt. Alternatively, a carbon resistor can also be used, however shunts are preferred due to the small tolerances and resistance of their properties (no drift). The measuring resistor is part of the measuring arrangement according to the invention and is connected in a suitable manner in series with the inverter which feeds the electric motor during normal operation.

According to one embodiment variant, a single measuring resistor can be used, through which all three motor phase currents flow. This results in a minimum installation space requirement in the motor electronics. The measuring resistor can be located before the inverter and connected to the upper intermediate circuit potential, or after the inverter and connected to ground.

According to an alternative embodiment variant, it is also possible to use more than one measuring resistor, in particular more than one shunt. Which according to one variant can be connected in parallel or in series. The series circuit through which all three motor phase currents flow has the following advantages: each of the series-connected measuring resistors provides a suitable measuring voltage which can be processed. The risk is thus minimized, so that when using a single measuring resistor, metal foreign bodies, for example metal chips, bridge the measuring resistor and no voltage is measured despite the current flowing through it. According to a further variant, each motor phase can correspond to its own measuring resistor, in particular a shunt, so that only the motor current of the respective phase flows to ground via each measuring resistor. A plurality of measurement voltages are therefore also present, corresponding to the number of measurement resistors, which can each be processed separately from one another in accordance with the method according to the invention.

The value of the measuring resistance, in particular the value of the shunt, is generally known. The motor current is then obtained according to ohm's law in the following way: the measured voltage drop is divided by the resistance value. If the measuring resistor has a resistance value of 1 Ω, for example, a motor current of 400mA results from a voltage drop of 400 mV. However, it is preferable to use very small measuring resistances, in particular less than 1 Ω, in order to keep ohmic losses (heat) to a minimum.

However, in order to implement the method according to the invention, it is not necessary to divide the voltage drop across the measuring resistor by the resistance value in order to obtain a corresponding current value in this way, since the actual motor current is not critical. It is therefore also possible to calculate the value of the voltage drop across the measuring resistor itself, which represents the previously mentioned variable independent of the motor current, since it is proportional to the motor current.

According to a preferred embodiment variant, the motor current and/or the variables related thereto can be determined via a first signal path for obtaining a first measured value and simultaneously via a second signal path for obtaining a second measured value, wherein one of the two measured values is inverted with respect to the other measured value. The first and second signal paths are preferably part of the measuring means. The two signal paths lead on the one hand to redundancy and on the other hand to be able to determine the validity or correctness of the two measured values as a result of the reversal of one of the two measured values. For example, a comparison of the first and second measured values with one another can be carried out and, if the measured signals are not in opposite directions to one another, an interruption of the voltage supply can be caused. Since in this case there is an error in one of the two signal paths, it is no longer ensured that: the temperature monitoring according to the invention works correctly.

According to an advantageous further development, the second signal path can comprise means for determining a time-interval-dependent maximum value of the motor current and/or the variable associated therewith, or the second measurement value represents a time-interval-dependent maximum value of the motor current and/or the variable associated therewith. In this way, for each time interval, for example a time interval of a length of between 50ms and 500ms, preferably a length of 100ms, a respectively occurring peak value of the motor current or of the variable is determined and used as an analog measured value for the respective time range. Determining, by the maximum value related to the time interval, to avoid: since the motor current is determined during the processing, in particular during the sampling of the rapidly changing first measured values, as a result of a beat error, which is smaller than the motor current actually present, it is possible to exclude: due to such a beat error, overheating of the motor remains unrecognized.

In order to improve the robustness of the method, a filtering can be carried out, in particular a running average in the case of the first and/or second measured values over a filtering time period. In this way, voltage peaks are filtered out, since they do not always feed energy into the electric motor.

The two measured values are stored in a suitable manner, so that a comparison between the measured values can be carried out. According to the standard, the measured values of the first signal path are used for the temperature monitoring according to the invention.

Preferably, a comparison of the first and second measured values with one another is carried out, so that a discrepancy of the anomaly pointing to an error can be identified. Since typically the two measurements should be substantially identical. And a deviation in the value will indicate an error. However, if in the second signal path a maximum value of the motor current and/or a variable related thereto is determined as a measured value, which is related to the time interval, this automatically causes a numerical deviation of the measured value. In order to ensure here: when the higher of the two measured values is always used as motor current and/or as a variable associated therewith, it makes sense to detect an excessive temperature.

Since time-interval-dependent measured values of the motor current and/or variables related thereto are used as measured values in the second signal path, only a numerical deviation of the measured values still does not indicate an error. However, errors in the processing of the measurement signals can be inferred if the deviation exceeds a certain tolerance, in particular greater than 10%, preferably greater than 15%.

According to one refinement, it can be provided that an error in the processing of the measurement signal is only detected if the tolerance remains exceeded for a certain observation period. The observation period can lie between 0.5s and 2s, preferably 1 s.

According to a preferred embodiment variant, a monostable tripping device can be used for controlling the tripping mechanism, which is triggered periodically, in particular by the control unit, during error-free operation of the electric motor, so that the output of the tripping device outputs a constant control signal in order to keep the tripping mechanism in the closed state. The interruption of the voltage supply can then be caused by: the triggering of the trigger is stopped. With regard to the circuit arrangement according to the invention, it can comprise a monostable trigger which controls the tripping mechanism and can be triggered by a control signal of a control unit, wherein the control unit is set up to periodically trigger the trigger in error-free operation of the electric motor and the trigger is set up to output a constant control signal by periodic triggering in order to keep the tripping mechanism in the closed state. The control unit is also correspondingly designed to stop the periodic triggering if the motor current and/or variables related thereto are above a limit value for one or more time periods. By means of the method or device development, a safety control circuit is implemented, by means of which the voltage supply to the electric motor is maintained only when there is no error, i.e. the trigger is always triggered again. The triggering is intentionally stopped if an excessive temperature is identified. However, the same can be done in every other error, either intentionally or automatically as well. If, for example, an error in the software is caused, by which the software no longer responds and "seizes", the triggering is stopped, so that a safe disconnection of the voltage supply is also achieved by the monostable trigger and the disconnection mechanism.

The circuit arrangement system according to the invention is also set up to carry out the method described above.

The invention finally also relates to an electric motor with motor electronics, which comprises a circuit arrangement according to the invention. Preferably, the electric motor is part of a centrifugal pump assembly, in particular a heated circulation pump assembly. Here, the electric motor may be configured as a wet rotor.

Drawings

Further features and advantages of the invention are explained below with reference to the drawings according to embodiments. In the drawings:

fig. 1 shows a layout system for protection against excessive temperatures according to the prior art;

fig. 2 shows an arrangement for protecting against excessive temperatures according to a first variant of the invention;

fig. 3 shows an arrangement for protecting against excessive temperatures according to a second variant of the invention;

fig. 4 shows the winding temperature in relation to the motor current in three current jumps;

fig. 5 shows the winding temperature in relation to the motor current in a fourth current step;

FIG. 6 shows an enlarged view of a portion of FIG. 5 during a current jump;

FIG. 7 shows a counter variation curve relating to motor temperature;

FIG. 8 shows a flow chart of a variant of the method according to the invention;

fig. 9 shows a flow chart of a further variant of the method according to the invention;

fig. 10 shows an arrangement for protecting against excessive temperatures according to a third variant of the invention.

Detailed Description

Fig. 1 shows an electric motor 1 according to the prior art together with an electronic device, in which protection against excessive temperatures is implemented in the motor winding 1 a. The electric motor 1 is connected to a mains voltage supply 11 via a rotational speed setter 3, which is designed here in the form of an inverter, and

further components

12, 13, 8. The rotational speed setter 3 comprises a rectifier 4, a voltage intermediate circuit 5 and an inverter 6, which are switched on in succession in a known manner, wherein the inverter 6 generates 3-phase voltages for the motor winding 1a from the intermediate circuit voltage, which are connected here purely exemplarily in a delta.

Connected upstream of the rotational speed setter 3 are an interference filter 8 (for example a PFC (Power Factor Control) for filtering higher harmonics), a switching current limiter 13 (for example in the form of a PTC (positive temperature coefficient)) and a safety device 12. The safety device 12, the switch-on current limiter 13 and the interference filter 8 are connected in series and connect the system voltage supply 11 to the rotational speed setter 3. A disconnection mechanism in the form of a disconnection relay 14 is provided in parallel with the switch-on current limiter 13, which according to regulations bridges the switch-on current limiter 13 after the electric motor 1 has been connected to the mains voltage supply 11.

The motor electronics furthermore comprise a control unit 10 which generates a PWM control signal (PWM) on the basis of the measured intermediate circuit voltage and the motor current and transmits it via a PWM control line 18 to the inverter 6, which switches its semiconductor switches on and off as a function of the PWM control signal in order to generate the phase voltages, the intermediate circuit voltage being supplied to the motor electronics via a measurement line 25, and the motor current being measured in the intermediate circuit via a measurement means 7 and being supplied via a measurement line 26. The control unit 10 also effects a speed regulation of the electric motor 1 in this case.

In order to provide the different components of the motor electronics with supply voltages, a low-voltage supply 9 is provided, which is supplied here by way of example by the intermediate circuit 5 and provides at least one supply voltage, which is conducted to the different components via

supply lines

20, 21, 22.

For temperature monitoring of the electric motor 1, a temperature sensor 2 in the form of a PTC or PT1000 is present between the motor windings 1a, the control signal of which directly controls the shut-off relay 14 via a control line 23. This means that: the value of the sensor signal has a direct effect on whether the cut-off relay 14 is open or closed. In the normal state, the temperature sensor 2 outputs, for example, a voltage value which keeps the cut-off relay 14 closed in the normal state.

Since other errors can also occur in the motor electronics or in the electric motor 1 itself, which must or should be responded to by disconnecting the mains voltage supply 11, the control unit 10 is also connected to the disconnection relay 14 via a corresponding control line 19. Likewise, the corresponding control signal is a voltage signal in the normal case, which keeps the shut-off relay 14 closed in the normal state.

In order to now open the shut-off relay in both cases (i.e. in the case of an excessively high temperature, which is signaled by the temperature sensor 2, but also in the case of further errors, which are signaled by the control unit 10), the two

control lines

19, 23 are coupled to one another via an and gate 15, wherein the output of the and gate 15 is connected via a corresponding switching line 27 to the control input of the shut-off relay 14. Alternatively, and gate 15 can also be formed by a logical and junction. Thus, for example, the control unit 10 can control the low-side switch for the relay 14, while the PTC 2 controls the high-side switch, so that the relay is switched on only when both are closed.

In the embodiment variant according to fig. 1, the motor temperature monitoring is implemented exclusively in hardware. No software components are present in the control unit 10 and in other components, which cause a current interruption of the motor winding 1a, i.e. an interruption of the voltage supply to the electric motor 1, in the event of an excessively high temperature. Since, for the temperature sensing element 2, a corresponding installation space must be present inside the stator accommodating the winding 1a, in which the temperature sensing element 2 must be arranged in a manner thermally well connected to the motor winding 1a, the construction and installation of the electric motor 1 together with the temperature sensing element 2 is relatively complicated. Furthermore, the necessity of the temperature sensor 2 causes additional costs.

Fig. 2 now shows a first embodiment variant according to the invention with a software-controlled, excessive temperature shut-off of the electric motor 1. The temperature sensor 2 can be dispensed with by the invention, which is therefore also applicable to the power supply line 22 and the control line 23, which are connected to the temperature sensor 2 beforehand.

According to the invention, the control unit 10 is supplemented by a motor temperature monitoring unit 16, which triggers an emergency shutdown of the voltage supply to the electric motor 1 if an excessive temperature is reached in the motor winding 1 a. For this purpose, the control thereof already has a motor current measurement value for controlling the inverter 6, from which motor current measurement value or its profile the motor temperature monitoring unit 16 estimates the motor temperature or the winding temperature purely quantitatively. This is explained below. Here, a specific calculation of the motor temperature is not necessary and therefore is not performed either.

The determined excessive temperature is processed in such a way that a corresponding signal is supplied by the control unit 10 to the cut-off relay 14 via the control line 19, which thus opens the cut-off relay 14 and interrupts the voltage supply from the mains voltage supply 11 to the electric motor 1, so that the motor winding 1a is not energized.

A further embodiment variant of the circuit arrangement according to the invention is shown in fig. 3. This differs from the first variant embodiment in that the system voltage supply 11 is not directly separated from the electric motor 1 or the rotational speed setter 3, but rather is a supply Voltage (VDD) which is supplied by the low-voltage supply 9 to the inverter 6, more precisely to the drive circuit 6a of the inverter 6. The same therefore occurs, interrupting the voltage supply to the electric motor, however indirectly. For this purpose, a disconnection mechanism 17 in the form of an electronic switching device is present between the low-voltage supply 9 and the inverter 6 (or its drive circuit 6a), which is controlled by the control unit 10, in particular by the motor temperature monitoring unit 16. In this embodiment variant, the interrupter relay 14 can therefore be dispensed with, which provides corresponding installation space in the motor electronics and which can therefore be produced more compactly and more cost-effectively.

Fig. 3 furthermore shows an alternative modification of the first variant of the embodiment, in that a non-volatile memory 24 (for example in the form of an electrically erasable programmable read-only memory EEPROMS) is connected to the control unit 10 in order to store values which are generated or processed in the context of the motor temperature monitoring, as will be explained below. The control unit 10 can be, for example, a microcontroller.

Fig. 4 shows the temporal course of four curves K1, K2, K3, K4 belonging to the first electric motor 1. Curve K1 shows the ambient temperature, curve K2 shows the temperature of the medium which is conveyed by the centrifugal pump driven by electric motor 1 and which flows through the wet-running rotor space of electric motor 1, and curve K3 shows the motor current I_MAnd curve K4 shows the motor winding temperature theta. The ambient temperature K1 fluctuates at approximately 70 ℃ and the medium temperature lies between 107 ℃ and 110 ℃, whereas the motor winding temperature θ in curve K4 is due to the motor current I_MA temperature of almost 190 c is reached. Motor current I_MIn this case, a number of sudden increases are made in order to check the temperature behavior, wherein a first sudden change to 250mA, a second sudden change to 300mA and a third sudden change to 350mA are made. As curve K4 shows, in each sudden change the temperature approaches a specific local maximum temperature progressively according to an exponential increase. The maximum temperature is about 143 deg. in the case of 250mA, about 162 deg. in the case of 300mA and about 188 deg. in the case of 350 mA. The local maximum temperature is therefore characteristic for the motor current set in each of the first electric motors 1.

Fig. 5 shows a current profile K3 for the second electric motor 1, which has a larger stator than the first electric motor. The motor current is first set in a height of 400mA and subsequently in a height of 750mA, wherein the current corresponds to the maximum motor current I of the second electric motor 1_M,max. The temperature curve K4 shows that at 400mA the motor winding temperature rises slightly above 160 c, for example 163 cWhile the maximum current causes the motor temperature to rise abruptly well above 200 ℃. The increase in the rise is shown in fig. 6.

FIG. 6 shows that a specific maximum temperature can be defined and that a predetermined limit temperature θ can be set_limStarting and determining: until a maximum current I is present_M,maxReaches the maximum temperature theta_maxHow long it takes. The time period R required for this is indicated in fig. 6 and represents the response time period for the emergency shutdown of the voltage supply in time after the approach of an excessive temperature. In this case, θ is determined according to the relevant standard (e.g. IEC60335 chapter 19, protection class 155 (F)))_maxTemperature of 180 ℃ as maximum temperature θ_max. In addition, a limit temperature theta is determined_limFrom this limit temperature, a critical observation of the motor temperature should be made 160 ℃. However, according to the invention, the observation is not carried out directly in the form of the motor temperature itself, but rather in order to observe the motor current I_M,Because each motor current value corresponds to a certain motor winding temperature θ, as shown in fig. 4 and 5. Therefore, the limiting temperature θ _lim160 ℃ in the first electric motor 1 is set to a specific limiting current I of approximately 300mA_M,limCorresponds (see fig. 4) and corresponds in the second electric motor 1 to a specific limit current of about 400mA (see fig. 5) or is slightly below it (about 380mA), from which value, instead of the limit temperature θ_limShould proceed to motor current I_MCritical observation of (2). This is achieved according to the invention by a counter X.

FIG. 7 illustrates the counter X as a function of the motor current I_MThe profile over time t. The upper curve in fig. 7 represents the motor current I_M(t) purely exemplary profile over time t. At the beginning of the current curve, the motor current I_MSlightly lower than rated current I_nennAnd then towards the limiting current I_M,limGradually increasing. Once the limiting current I is reached_M,limThen the counter X is counted up. This will always be for a time period T₁As long as the limit temperature I is kept exceeded_M,lim. If the motor current I_MAgain below the limiting current I_M,limThen the risk of too high a temperature is removed again first, since the motor winding temperature θ is reduced. This is considered as follows: counter X for motor current I_MBelow the current limit value I_M,limIs gradually reduced, see time period T₂. Because the cooling ratio of the electric motor 1 is at its maximum motor current I_M,maxThe heating in the case of (2) is carried out more slowly, wherein the time constant for the counter X to decrease is smaller than the time constant for the counter X to increase, is calculated with different time constants when the counter X increases and decreases.

The reduction of the counter X in the time period T2 continues as long as the motor current I_MKept below the limiting current I_M,lim. If the limit current is exceeded again, the counter X is incremented again, see time period T₃Until the limit value I is again undershot_M,limThis causes a re-reduction of the counter X, see time period T₄. During this period T4, the limiting current I is kept lower_M,limSo that the counter X is completely reduced until zero, i.e. the motor current I previously passed through the motor 1_MThe heat applied during the time period T₄Again the end of (a) is completely eliminated. Subsequently, however, in the example according to fig. 7, the motor current I_MAgain above the limit value I_M,limAnd more precisely for the duration of the time period T5, which causes the counter X to rise up to a maximum value X_max. The maximum counter reading X_maxThe reaching of (b) causes the voltage supply to the electric motor 1 to be interrupted, for example according to the variant in fig. 2 or 3, so that the motor winding 1a cuts off the current and no further heat is input into the electric motor 1. Thereby, the motor current I_MAgain becomes zero and the counter or motor temperature slowly decreases again, as can be recognized from the change shown in fig. 7 in the counter reading and only part of the current curve in time period T6.

The flow of the method according to the invention according to one embodiment variant is illustrated in fig. 8. Which measures the motor current I_MAt the beginning, the stepsS1, the motor current is then checked as follows: whether it is greater than a limit value I_M,limSee step S2. If this is the case, the counter X is incremented by the value X_aSee step S3. If the value is understood to be the current-time value I_aΔ t, i.e. understood as the increment I per unit time Δ t_aIt is clear that a counter can also be understood as a current-time integration.

Check after the counter is incremented: whether or not the maximum counter reading X is reached_maxSee step S4. If this is not the case, the method continues at its beginning. However, the execution of the method can be performed periodically, for example, every 100ms, so that there can be a corresponding waiting tile between step S4 and step S1 in order to wait for the end of the current period.

If the check in step S4 reveals: the counter X reaches its maximum counter reading X_maxThen the voltage supply is interrupted as set forth in fig. 7, see step S5. The method thus ends, see S7. Alternatively, the motor temperature monitoring can also be continued during the interruption of the voltage supply, in order to be able to identify: whether and when the motor winding temperature again reaches a non-critical value. This possibility can be achieved in particular by means of the embodiment variant in fig. 3, in which only the supply voltage of the inverter 6 or its drive logic 6a is interrupted in order to switch off the motor windings, while the motor electronics remain supplied with power.

If the motor current I_MThe measurements of (a) show that: in step S2, limit value I is not exceeded_M,limThen the counter X is decremented by the value X_bSee step S6. To avoid negative counter values, two values "zero" and "X-X" are used in step S6_bThe larger value of "is used as the new counter reading.

Fig. 9 shows an alternative embodiment variant of the method. Here, the same steps are denoted by the same reference numerals as in fig. 8. The method according to fig. 9 differs from the method in fig. 8 in that, before the counter X is incremented, the query: whether or not maximum counter reading is reachedX_max(step 4), and only if the maximum counter reading X has not been exceeded_maxThe counter X is incremented only.

As a further difference, in step S6 the counter X is decremented by the value X_bThe search for the included maximum is divided into two single steps S6a and S6 b. In the variant in fig. 9, therefore, the query is first carried out: whether the counter reading X is still greater than zero. If this is not the case, the counter X does not have to be further decreased and the method ends or continues forward. And if the counter X is greater than zero, then the value X is decremented_bSee step S6 b.

As an additional supplement, in the embodiment variant according to fig. 9, a check is considered: whether counter X has fallen below X_maxWhich allows to cancel the interruption, step S9, i.e. allows to restore the

voltage supply

11, 9 to the electric motor 1. The limit Y can be, for example, a maximum counter reading X_maxFor example, 70% (Y ═ 0.7). The voltage supply is then resumed, but at the same time the counter reading X is also decreased, step S6 b. Once the current cycle ends or the next cycle begins, the method continues again at step S1.

Fig. 10 shows a detailed view of the hardware components of the circuit arrangement system according to the invention. The electric motor 1, which is illustrated purely by way of example as a Permanent Magnet Synchronous Motor (PMSM), is fed by a rotational speed setter 3, which is connected to the grid voltage supply 11 via a safety device 12 and a switching current limiter in the form of a PTC 13. The securing device 12 connects the rotational speed setting device 3 to the mains voltage supply 11, while the PTC13 is connected to the neutral line of the mains voltage supply 11. The rotational speed setter 3 comprises a rectifier 4, a voltage intermediate circuit 5, illustrated here by a capacitor, and an intermediate circuit potential V_BThe connected inverter 6 is fed by the voltage intermediate circuit 5. A further safety device 12a is present between the intermediate circuit 5 and the inverter 6.

The inverter 6 is formed by a plurality of switchable power semiconductors 6b and a drive circuit 6a (drive logic), wherein the power semiconductors 6b, for example MOSFETs, are driven by means of a driveThe circuit 6a is controlled in such a way that the three phases of the electric motor 1 are brought into contact with the intermediate circuit potential V according to a defined sequence_BAnd (4) connecting. Each semiconductor switch 6b is assigned an own driver of the driver circuit 6 a. If necessary, the driver and the associated semiconductor switch 6b can also be constructed as a unit. In the example according to fig. 10, there are six semiconductor switches 6b, wherein each two semiconductor switches 6b feed one phase of the electric motor 1 and are connected in series to form a full bridge (Vollbr üke) and the nodes between them form the feed connections of the respective motor phases. Each semiconductor switch 6b is thus in one half bridge. Each diode is connected in anti-parallel with the semiconductor switch 6b and conducts a ring current during commutation of the motor voltage from one half-bridge to the next. If one of the upper semiconductor switches 6b is switched on, the respective motor phase is brought into contact with the intermediate circuit potential V_BAnd (4) connecting. If one of the lower semiconductor switches 6b is on, the motor phase is connected to Ground (GND). Methods for controlling the semiconductor switches of such inverters are well known, so that reference is made to the relevant literature in this regard.

The inverter 6 is connected to Ground (GND) via a single measuring resistor 7a (here in the form of a shunt). Instead of a single shunt, two or three measuring resistors can be used, which can be connected in parallel or in series. The measuring resistor 7a is part of the measuring means 7, as shown in fig. 2 and 3. Motor current I_MVia the voltage drop Us across the measuring resistor 7 a. The voltage Us at the measuring resistor 7a is supplied to an operational amplifier 7b, which here forms a measuring amplifier and provides a first measured value U at its output₁The first measured value is supplied to the control unit 10, in particular to the motor temperature monitoring unit 16. For the first measured value U₁Is a first signal path 30 from the measuring resistor 7a to the respective input of the control unit 10. Except for the first measured value U₁Besides, the second measured value U₂Via a second signal path 31 and is supplied to the control unit 10 or the motor temperature monitoring unit 16. Second measured value U₂And a first measured value U₁The comparison is reversed (invertier). The two

signal paths

30, 31 thus provide not only safety due to redundancy, but rather also enable the correctness of the measured values U1, U2 to be evaluated on the basis of the reversal in the scope of the plausibility check. This makes it possible to detect errors in the analog measured values U1, U2 in the analog-to-digital conversion (in the ADC) in the control unit 10.

The first and

second signal paths

30, 31 have the same origin, i.e. the voltage drop Us at the measuring resistance 7 a. The second signal path 31 comprises an operational amplifier 7c and means 7d for determining a maximum value associated with a time interval. The operational amplifier 7c first amplifies the measurement voltage of the measurement resistor 7a and then feeds it to the device 7d in order to determine the maximum value. The device 7d likewise comprises an operational amplifier 71 which is externally wired in such a way that its output signal always corresponds to the maximum value of the input signal within a specific time interval, which is likewise determined by external wiring (RC element). This is done by appropriately dimensioning the resistor 73 and the capacitor 74 connected in parallel therewith at the output of the operational amplifier 71 after the diode 72, wherein the common node of the capacitor 74, the resistor 73 and the cathode terminal of the diode 72 is connected via a feedback branch 75 with the negative input of the operational amplifier 71. Here, for the sake of simplicity, other components in the feedback branch 75 that cause signal amplification are not shown. The output signal U of the maximum value determining device 7d is fed back to the negative operational amplifier input_SAIn addition to the input signal U_SEAnd reversing.

The mode of action of the maximum value determination unit 7d is shown in fig. 10 below the device 7 d. For each time interval, e.g. every 100ms, the analog input signal U is determined during the time interval_SE(t) maximum value. However, due to the inversion, a first maximum value at the input in the first interval (which is larger than a second maximum value at the input in the second interval) causes a first maximum value at the output of the first interval, which is smaller than a second maximum value at the output of the second interval. For maximum correlation with time intervalAnalog output signal U of value-determining device 7d_SA(t) for each time t a second measured value U is indicated₂Said second measured value is fed to the control unit 10 or the motor temperature monitoring unit 16. The two measured values U1, U2 are analog values and are converted into digital values in the control unit 10 by means of an AD converter.

Input signal U shown in fig. 10 below device 7d_SE(t) and corresponding output signal U_SAThe corresponding profile of (t) is merely used to illustrate the mode of action of the device 7 d. However, the curve does not represent the motor current I_M(t) actual change. The actual change is very "jumping" because no constant current flows through the shunt 7a during normal (PWM) operation of the inverter 6, but only one phase current is visible at one point in time, and the combination (addition/difference) of the two phase currents is visible at another point in time, depending on the switching state of the semiconductor switch 6 b. Thus the first measured value U₁With a relatively unstable and abrupt change profile, and the second measured value comprises a range-wise constant, but inverted measured value U_SA(t), but here the reversal can also be reversed again in terms of software.

In the motor temperature monitoring unit 16, the first and second measured values U are now carried out₁、U₂Enables identification of anomalous differences that indicate a fault. In this case, the motor temperature monitoring unit 16 is again controlled by the inverted signal U₂Calculating non-reverse motor current I_M. To monitor the motor temperature θ, two measured values U are used₁、U₂The numerically larger measurement. This ensures that: without excessive temperatures remaining undetected as a result of timing errors, by which an excessively low motor current I in the control unit 10 is always measured_M. If measured value U₁、U₂If the values deviate by more than 15% from one another within a defined observation period of, for example, 1s, then an error in the processing of the measured values is inferred and the voltage supply is likewise interrupted for safety.

The motor temperature monitoring unit 16 is also based on the measured value U₁Or based on measurements, if necessaryMagnitude U₂The method according to the invention, in particular the method steps S2 to S9 according to fig. 8 or 9, is carried out and the disconnection unit 17, which is designed here in the form of an electronic switching device, is controlled as a function of the counter reading X. The electronic switching device comprises two series-connected individual switches 29A, 29B in the form of bipolar transistors 29A, 29B, respectively, which are supplied with the same control signal K_AControlled and located between the low voltage supply 9 and the input for the supply voltage VDD of the drive circuit 6a of the inverter 6, so that the drive circuit 6a is supplied with voltage only when both

single switches

29a, 29b are on. The double implementation of the

individual switches

29a, 29b is again used here as redundancy. Thus ensuring that: in the event of a defect in one of the

individual switches

29a, 29b, the voltage supply device VDD can be interrupted at least by the other individual switch.

By interrupting the low-voltage supply 9, the driver circuit 6a can no longer switch on the semiconductor switch 6b or keep it switched on, since a control voltage is required for this purpose. Thus, the motor winding 1a is maintained at the intermediate circuit voltage V_BSeparate and then not energize.

The electronic switching device 17 comprises a monostable flip-flop 28, also commonly referred to as a monostable flip-flop, which generates at its output a control signal K for the

individual switches

29a, 29b_A. When a pulse, a so-called flip-flop, reaches the input, the control signal K_AIs a single pulse of a particular duration. According to the invention, the control unit 10, in particular the motor temperature monitoring unit 16, uses the trigger signal K_EControlling the trigger 28, the trigger signal being formed by a series of trigger pulses whose time intervals are smaller than the duration of the individual pulses of the trigger 28, so that the trigger signal K is applied only_EThen flip-flop 28 provides an output signal that is continuous, as it were. The electronic switching device 17 thus implements a safety control circuit (Totmann-Schaltung) which maintains the voltage supply only when it signals that everything is normal once and again.

If the motor temperature monitoring unit 16 determines that an excessive temperature is approaching, the trigger is stoppedSignalling K_E. Thus, the pulse of the flip-flop 28 ends and the two

individual switches

29a, 29b are no longer switched on. The supply voltage for the drive circuit 6a is thus interrupted.

In addition to the electronic switching device 17, in the variant of embodiment according to fig. 10, the disconnection relay 14 is also arranged in parallel with the PTC13 in order to bridge the electric motor after it has been connected to the mains voltage supply 11, since the motor 1 would otherwise not start due to the current received and the resulting high resistance of the PTC 13. In order to be able to draw the current that is usual during operation of the intermediate circuit 5, the disconnection relay 14 is closed after the connection to the electrical network 11 has been established, in particular when the motor electronics are started. For this purpose, a MOSFET transistor 14a is used, which is controlled by the control unit 10 and connects the switching input of the shut-off relay 14 to Ground (GND). Alternatively, the transistor 14a can connect the relay 14a to the low-voltage supply device 9.

It is not necessary, but possible, to open the shut-off relay 14 as a further safety measure when there is an error in the motor electronics or in the electric motor 1 itself. The electronic switching device 17 or another such switching device therefore connects the voltage supply 9 to the shut-off relay 14 in the event of an error, in particular when an excessive temperature is approached, in addition to or as an alternative to the supply voltage of the inverter 6, in order to shut off the current to the motor winding 1 a.

The control unit 10 is connected in a data-technical manner to the non-volatile memory 24. In the non-volatile memory, for example, the current counter reading of the counter X can be saved and/or the measured value U can be maintained₁、U₂For subsequent comparison. The storage of the counter reading has the following advantages: the counter reading continues after the

voltage supply

9, 11 is interrupted and can then be used as a starting value for the counter. Thereby avoiding: the motor temperature monitoring unit 16 loses temperature information by interrupting the voltage supply and operates with an incorrect starting value of zero when the power supply is reversed, although the motor may already have a temperature above the temperature limit value. This is possible, for example: before the limit temperature is reached, but before it is exceeded forThe limit value of the motor current or a variable associated therewith has previously switched off the electric motor or interrupted the supply of power either by another error or by manual influence.

According to the invention, the motor current I is measured in each operating state of the electric motor 1_MIn particular also when the motor 1 or its electronics are in a standby mode, i.e. a standby mode, the motor 1 is not rotated but is ready for this purpose. If one of the semiconductor switches 6b of the inverter 6 has a defect, which is usually manifested in the semiconductor switch as a short circuit or so-called "partial on", i.e. a limited on-resistance, not controlled via the gate or base, between the power terminals (drain-source, emitter-collector), a leakage current can flow through the motor, which can be identified by measuring the motor current and comparing it with a prepared limit value.

Thus, according to one embodiment variant, the control unit 10 is set up to determine, in the preparation mode: whether the motor current is greater than a readiness limit. If this is the case, the control unit is provided for individually switching on the semiconductor switches 6b one after the other. If a defect or a short circuit is present in one of the semiconductor switches 6b, the intermediate circuit potential V is caused by switching on the semiconductor switch connected in series with the defective semiconductor switch in the same full bridge_BShort-circuiting to ground or via the measuring resistor 7 a. This in turn causes a short-circuit current, by means of which the fuse 12, 2a triggers or the motor temperature monitoring according to the invention initiates an emergency shut-off of the voltage supply as a result of the approach to an excessive temperature.

The invention is not limited to the specific embodiment variants described. It is instead clear to the person skilled in the art that the circuit-arrangement system according to the invention and the method according to the invention can be modified in an arbitrary, close manner without departing from the basic idea of the invention. Thus, it can be used in different motor types than a PMSM, for example, and can be transferred to a generator and/or to an arbitrary rotational speed setter. Alternatively to the measurement by means of a measuring resistance, the motor current can also be calculated from other variables or can even be estimated on the basis of a mathematical model of the electric motor. The low-voltage supply device 9 is able to also generate two or more different supply voltages as required and to supply them to the respective components as required. The intermediate circuit 5 can likewise be designed arbitrarily, for example symmetrically, with, for example, two capacitors, so that a positive or negative intermediate circuit voltage can be switched to the motor windings. For this purpose, the inverter can have two semiconductor switches per half bridge, i.e. a total of 12 semiconductor switches, in a known manner. It is also possible that, instead of an up-counting counter, a down-counting counter can be implemented. In this case, the above-described steps are then exchanged accordingly when the limit value is exceeded or undershot.

List of reference numerals

1 electric motor

1a motor winding

2 temperature sensor, PTC

3 speed regulator, frequency converter

4 rectifier

5 voltage intermediate circuit

6 inverter

6a drive circuit

6b semiconductor switch

7 measuring mechanism for motor current

7a measuring resistance, shunt

7b operational amplifier

7c operational amplifier

7d device for determining a maximum value associated with a time interval

71 operational amplifier

72 diode

73 resistor

74 capacitor

75 feedback branch

8 interference filter

9 low pressure supply device

10 control unit

11 network voltage supply device

12 safety device

12a safety device

13-turn-on current limiter

13a modified on-current limiter

14 breaking mechanism, electromechanical switch, breaking relay

14a transistor, MOSFET

15 AND gate

16 motor temperature monitoring unit

17 breaking mechanism, electronic switch device

18 PWM control circuit

19 control circuit from control unit to circuit breaking mechanism

20 supply line to speed setter/inverter

21 supply line to control unit

22 power supply to temperature sensor

23 control circuit from temperature sensor to cut-off relay

24 non-volatile memory

25 measuring circuit for intermediate circuit voltage

26 measuring circuit for motor current

27 switching line from and gate to trip relay

28 monostable flip-flop

29a Single switch, transistor

29b Single switch, transistor

30 first signal path

31 second signal path

Claims

1. Method for protecting an electric motor (1) against excessive temperatures, in which the voltage supply (9, 11) is interrupted in the event of an error by opening a tripping mechanism (14, 17), characterized in that the reception of a fault by the electric motor (1) is determined and checkedMotor current (I)_M) And/or a variable (U) related to the motor current_s) When the motor current (I) is not interrupted for a certain period of time_M) And/or a variable (U) related to the motor current_s) Continuously above a limit value (I)_M,lim) The motor current and/or a variable related to the motor current is/are continuously higher than the limit value (I) at any time or in each of a plurality of interrupted time intervals_M,lim) When the maximum motor current (I) is lower than the limit value, the interruption is performed_max) Or the motor current (I)_M) Related variable (U)_s) To a value corresponding thereto.

2. Method according to claim 1, characterized in that said limit value (I)_M,lim) At maximum motor current (I)_M,max) 1/3 and 2/3.

3. Method according to claim 1 or 2, characterized in that the interruption is caused in a software-controlled manner, wherein the motor current (I) is repeated periodically_M) And/or the variable (U) related to the motor current_s) With the limit value (I)_M,lim) Comparison of (1).

4. Method according to claim 1, characterized in that when the motor current (I) is present_M) And/or the variable (U) related to the motor current_s) When the limit value is exceeded, a counter (X) is incremented, when the counter (X) reaches a maximum counter reading (X)_max) If so, the voltage supply (9, 11) is interrupted.

5. Method according to claim 1, characterized in that when the motor current (I) is present_M) And/or the variable (U) related to the motor current_s) When the limit value is exceeded, the counter (X) reads (X) from the maximum counter_max) Is decreased and when the counter (X) reaches a zero value, the voltage supply (9, 11) is interrupted.

6. Method according to claim 4 or 5, characterized in that said maximum counter reading (X)_max) Corresponding to or less than a time period at the maximum motor current (I)_M,max) From a determined limit temperature (theta) with flow_lim) Continues until the maximum permissible temperature (theta) of the electric motor (1) is reached_max)。

7. Method according to claim 4, characterized in that when the motor current (I) is present_M) And/or the variable (U) related to the motor current_s) Below the limit value (I)_M,lim) When so, the counter (X) is decremented.

8. The method of claim 7, wherein the counter is decreased only when the counter (X) is greater than zero.

9. Method according to claim 5, characterized in that when the motor current (I) is present_M) And/or the variable (U) related to the motor current_s) Below the limit value (I)_M,lim) The counter (X) is incremented.

10. Method according to claim 9, characterized in that it is only if the counter (X) is less than the maximum counter reading (X)_max) The counter is incremented.

11. Method according to claim 7, characterized in that the step (X) of the counter (X) increasing per unit time when a limit value is exceeded is_a) Corresponding steps (x) of the counter decreasing per unit time than if the limit value was undershot_b) And higher.

12. Method according to claim 9, characterized in that the counter (X) decreases by a higher step per unit time when the limit value is exceeded than the corresponding step per unit time the counter increases when the limit value is undershot.

13. Method according to claim 7, characterized in that it is only when the counter (X) is lower than the maximum counter reading (X)_max) Is detected, the interruption of the voltage supply (9, 11) is again cancelled.

14. Method according to claim 7, characterized in that it is only when the counter (X) is lower than the maximum counter reading (X)_max) At least 50%, the interruption of the voltage supply (9, 11) is again cancelled.

15. Method according to claim 9, characterized in that it is only when the counter (X) is higher than the maximum counter reading (X)_max) Is detected, the interruption of the voltage supply (9, 11) is again cancelled.

16. Method according to claim 9, characterized in that the maximum counter reading (X) is only reached when the counter (X) has reached again_max) At least 50%, the interruption of the voltage supply (9, 11) is again cancelled.

17. Method according to claim 4 or 5, characterized in that when establishing the voltage supply (9, 11) of the electric motor (1), a counter reading is stored and used as a starting value for a counter (X).

18. Method according to claim 4 or 5, characterized in that when the voltage supply (9, 11) of the electric motor (1) is restored, a counter reading is stored and used as a starting value for a counter (X).

19. Method according to claim 1, characterized in that the interruption of the voltage supply (9, 11) is caused by interrupting the supply Voltage (VDD) to the drive circuit (6a) of an inverter (6) which feeds the electric motor (1) in normal operation, by means of an electronic switching device (17).

20. Method according to claim 1, characterized in that the motor current (I) is also determined and checked in a standby mode of the electric motor (1)_M) And/or the variable (U) related to the motor current_s) And when in ready mode the motor current (I)_M) And/or the variable (U) related to the motor current_s) When a readiness limit value is exceeded, the semiconductor switches (6b) of an inverter (6) which feeds the electric motor (1) in normal operation are individually switched on in sequence.

21. Method according to claim 1, characterized in that the motor current (I) is_M) And/or the variable (U) related to the motor current_s) By means of a first measuring device for obtaining a first measured value (U)₁) Is determined and simultaneously used for obtaining a second measured value (U) via a first signal path (30)₂) Is determined, wherein the two measured values (U) are determined₁、U₂) Relative to the two measured values (U)₁、U₂) The other measurement in (a) is reversed.

22. Method according to claim 1, characterized in that a monostable trigger (28) is used for controlling the tripping mechanism (14, 17), which trigger is triggered periodically in error-free operation of the electric motor (1) in such a way that the output of the trigger (28) outputs a constant control signal (K)_A) In order to keep the breaking mechanism (14, 17) in a closed state and to cause interruption of the voltage supply by: -stopping triggering of the trigger (28).

23. Method according to claim 2, characterized in that the limit value (I)_M,lim) Corresponding to the following maximum motor current (I)_M,max) Not exceeding a determined limit temperature (theta) when the maximum motor current is applied without interruption_lim)。

24. Circuit arrangement for protecting an electric motor (1) against excessive temperatures, having a shut-off mechanism (14, 17) for interrupting a voltage supply in the event of an error, characterized in that a device for determining a motor current (I) received by the electric motor (1) is provided_M) And/or a variable (U) related to the motor current_s) And is provided with a measuring mechanism (7) for checking the motor current (I)_M) And/or the variable (U) related to the motor current_s) Wherein the control unit (10) is set up to control the tripping mechanism (14, 17) such that the motor current (I) flows during a specific uninterrupted time period_M) And/or the variable (U) related to the motor current_s) Continuously above a limit value (I)_M,lim) The motor current and/or a variable related to the motor current is continuously above a limit value (I) at times or for a plurality of interrupted periods_M,lim) When the voltage supply is interrupted, the limit value is less than the maximum permissible motor current (I)_M,max) Or with the motor current (I)_M) Related variable (U)_s) To a value corresponding thereto.

25. Circuit arrangement according to claim 24, characterized in that the measuring means (7) comprise means for obtaining a first measured value (U)₁) And a first signal path (30) for obtaining a second measurement value (U)₂) Wherein the two measured values (U) are transmitted to the second signal path (31) of (1)₁、U₂) Relative to the two measured values (U)₁、U₂) The other measurement in (a) is reversed.

26. The circuit arrangement according to claim 24, characterized in that the breaking mechanism (14, 17) is an electronic switching device via which in its closed state a drive circuit (6a) of an inverter (6) feeding the electric motor (1) in normal operation is connected with a voltage supply device (9).

27. The circuit arrangement according to claim 26, characterized in that the electronic switching device is at least one controllable semiconductor switch (29a, 29 b).

28. The circuit arrangement according to claim 24, characterized in that a monostable trigger (28) is provided which controls the tripping mechanism (14, 17), which trigger can be triggered by a trigger signal (K) of a control unit (10)_E) Triggering, wherein the control unit (10) is designed to periodically trigger the trigger (28) in error-free operation of the electric motor (1), and the trigger (28) is designed to output a constant control signal (KA) by means of the periodic triggering in order to keep the tripping mechanism (14, 17) in the closed state, and the control unit (10) is designed to switch off the motor current (I)_M) And/or the variable (U) related to the motor current_s) Above a limit value (I) for a certain period of time without interruption or for a plurality of periods of interruption_M,lim) And stopping the periodic triggering.

29. Electric motor having motor electronics comprising a circuit arrangement according to one of claims 24 to 28.

30. The electric motor of claim 29, wherein the electric motor is an electric motor of a centrifugal pump assembly.